diff --git a/nixos/lib/eval-config.nix b/nixos/lib/eval-config.nix
index 77490ca3762..9892d6f160f 100644
--- a/nixos/lib/eval-config.nix
+++ b/nixos/lib/eval-config.nix
@@ -41,6 +41,12 @@ let
       # default to the argument. That way this new default could propagate all
       # they way through, but has the last priority behind everything else.
       nixpkgs.system = lib.mkDefault system;
+
+      # Stash the value of the `system` argument. When using `nesting.children`
+      # we want to have the same default value behavior (immediately above)
+      # without any interference from the user's configuration.
+      nixpkgs.initialSystem = system;
+
       _module.args.pkgs = lib.mkIf (pkgs_ != null) (lib.mkForce pkgs_);
     };
   };
diff --git a/nixos/modules/misc/nixpkgs.nix b/nixos/modules/misc/nixpkgs.nix
index afb74581e23..011d493c153 100644
--- a/nixos/modules/misc/nixpkgs.nix
+++ b/nixos/modules/misc/nixpkgs.nix
@@ -216,6 +216,14 @@ in
         Ignored when <code>nixpkgs.pkgs</code> is set.
       '';
     };
+
+    initialSystem = mkOption {
+      type = types.str;
+      internal = true;
+      description = ''
+        Preserved value of <literal>system</literal> passed to <literal>eval-config.nix</literal>.
+      '';
+    };
   };
 
   config = {
diff --git a/nixos/modules/system/activation/top-level.nix b/nixos/modules/system/activation/top-level.nix
index f67d2900561..14bd751ce32 100644
--- a/nixos/modules/system/activation/top-level.nix
+++ b/nixos/modules/system/activation/top-level.nix
@@ -15,6 +15,7 @@ let
     map (childConfig:
       (import ../../../lib/eval-config.nix {
         inherit baseModules;
+        system = config.nixpkgs.initialSystem;
         modules =
            (optionals inheritParent modules)
         ++ [ ./no-clone.nix ]
diff --git a/nixos/tests/nesting.nix b/nixos/tests/nesting.nix
index 6388b67a6e4..a75806b24ff 100644
--- a/nixos/tests/nesting.nix
+++ b/nixos/tests/nesting.nix
@@ -29,10 +29,10 @@ import ./make-test-python.nix {
         )
         clone.succeed("cowsay hey")
         clone.succeed("hello")
-    
-        children.wait_for_unit("default.target")
-        children.succeed("cowsay hey")
-        children.fail("hello")
+
+    children.wait_for_unit("default.target")
+    children.succeed("cowsay hey")
+    children.fail("hello")
 
     with subtest("Nested children do not inherit from parent"):
         children.succeed(